More of this Feature • Page 2: Drawing: Lines • Page 3: Drawing: Shapes • Page 4: Draw vs. Paint • Page 5: Handles and Stuff • Page 6: Pictures: TBitmap • Page 7: Ways To Kill Flicker • Page 8: GDI, The Hard Way • Page 9: API Drawings

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Article submitted by: Alistair Keys

   Umm, GDI You Say?
GDI stands for Graphics Device Interface, and is the interface that Windows uses for drawing 2D graphics. It is also, unfortunately, the slowest method around, but is useful for basic graphics. This tutorial will introduce you to some of the jargon and terms in the GDI.

The first point to note is that you should not attempt to use the GDI for any fancy graphical effects, like cross-fading pictures, as it is a bit primitive. For professional-looking graphics try using DirectX, OpenGL, or a graphics library (e.g. any of these, among others: DelphiX, FastLib, DIBUltra, Graphics32...). However, you can use the GDI for some neat effects, with a little creativity.

   Anything Else I Should Know?
One common acronym you will find with GDI is DC ("Device Context"). This is what you draw on, and is represented in Delphi by TCanvas. The idea behind device contexts is to abstract the output device details, so you can use the same drawing functions for (e.g.) a screen or a printer.

Another (pretty important) note is that you will start by using the standard Delphi graphics functions, as these are wrappers for the GDI functions of Windows. When the need arises, I will describe the Windows GDI functions for which Delphi provides a nice interface.

   Enough Jargon! Let's Draw!
Patience, my friend. You will be drawing pretty pictures soon enough. First, you need to know a little about how the GDI is organized. Here are some classes of importance:

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